Microsoft Corp. (MSFT) Chairman Bill Gates has agreed to pay $800,000 for violating antitrust regulations in two stock purchases, U.S. antitrust authorities said on Monday.

The Federal Trade Commission (search) said it had reached a settlement with Gates resolving charges that he failed to properly notify antitrust officials about his acquisition of voting securities of Republic Services Inc. (RSG) in 2001 and ICOS Corp. (ICOS) settled with Microsoft in 2001.

The general counsel for Gates' private investment fund said in a statement that the problem was the result of a mistake and that Gates was never personally involved in the transactions.

General Counsel Mark Beatty said the fund, Cascade Investment LLC, had put new procedures into effect "to avoid this type of oversight in the future."

Gates bought shares in trash-hauling company Republic Services in November 2001. The transaction put his holdings over a 10 percent threshold that required antitrust notification, the FTC said.

But Gates failed to notify antitrust authorities, believing he was exempt from the requirement because the acquisition was only for investment purposes.

Gates later made a corrected filing in the case, and the FTC declined to seek any penalties.

But six months later, Gates violated the rules again when he bought shares in ICOS, co-maker of the new impotence treatment Cialis, according to the FTC. Once again, Gates thought he was exempt from the regulation.

The FTC said it sought substantial penalties for the second mistake.

"This case demonstrates the need to become fully aware of the reporting requirements of the HSR (Hart-Scott-Rodino) Act," Barry Nigro, deputy director of the FTC's Bureau of Competition, said in a statement.